Phosphor composition

Abstract

A method is disclosed for forming a blended phosphor composition. The method includes the steps of firing precursor compositions that include europium and nitrides of at least calcium, strontium and aluminum, in a refractory metal crucible and in the presence of a gas that precludes the formation of nitride compositions between the nitride starting materials and the refractory metal that forms the crucible. The resulting compositions can include phosphors that convert frequencies in the blue portion of the visible spectrum into frequencies in the red portion of the visible spectrum.

The invention claimed is: 
     
       1. A method of making a phosphor composition, the method comprising:
 forming a powder mixture comprising Ca 3 N 2 , Sr 2 N, AlN, Si 3 N 4  and
 a europium source composition; 
 
 heating the powder mixture at or near atmospheric pressure in the presence of a forming gas mixture comprising nitrogen and hydrogen; and 
 forming from the powder mixture a first phase comprising a nitride phosphor having a nominal composition of Ca 1-x-y Sr x Eu y AlSiN 3 , where 0<x<1 and 0<y<1, and a second phase comprising silicon aluminum oxynitride. 
 
     
     
       2. The method according to  claim 1  comprising:
 heating the powder mixture in a refractory crucible that is substantially inert in the presence of the forming gas mixture for a time sufficient to produce a phosphor composition that will down convert photons in the blue and ultraviolet regions of the spectrum into photons in the longer wavelength regions of the visible spectrum. 
 
     
     
       3. The method according to  claim 1 , comprising heating the powder mixture at atmospheric pressure. 
     
     
       4. The method according to  claim 1 , wherein the powder mixture is heated to a temperature of between about 1500 to 180° C. 
     
     
       5. The method according to  claim 1  wherein the silicon aluminum oxynitride comprises Si 2 Al 4 O 4 N 4 . 
     
     
       6. The method according to  claim 1  wherein the forming gas mixture comprises between about 5% and 10% hydrogen and a balance nitrogen. 
     
     
       7. The method according to  claim 1  wherein x is between about 0.5 and 0.7. 
     
     
       8. The method according to  claim 7  wherein x is between about 0.55 and 0.67. 
     
     
       9. The method according to  claim 1  wherein y is between about 0.013 and 0.017. 
     
     
       10. The method according to  claim 1  wherein the forming gas mixture includes about 95% nitrogen and about 5% hydrogen. 
     
     
       11. The method according to  claim 1  wherein the heating is carried out at a temperature of 1750° C. 
     
     
       12. The method according to  claim 1  wherein the heating comprises at least three heating steps at increasingly higher temperatures. 
     
     
       13. The method according to  claim 12  comprising a first heating step at 800° C., a second heating step at 1200° C., and a third heating step above 1600° C. 
     
     
       14. The method according to  claim 13  wherein ramping steps of about 350° C. per hour are employed between the first, second and third heating steps. 
     
     
       15. The method according to  claim 13  wherein the first and second heating steps are carried out for one hour each, and wherein the third heating step is carried out for two hours.